**Abstract**

The effects of prefermentative cold skin-contact technique using Malvasia *aromatica* were studied as a first step to adapt to the climate change related effects in order to intensify the aroma potential of white wines of the D.O. "Vinos de Madrid" keeping the organoleptic characteristics of the region. Major volatile compounds were extracted by liquid–liquid extraction and quantified by GC-FID. Minor volatile compounds were determined by HS-SPME/GC–MS. Sensory analysis were also carried out to describe and quantify attributes of the wines. A total of 37 components were identified and quantified. Volatile components showed mixed behavior depending on the skin-contact time. Skin-contact for longer helps to enhance the floral character provided by some compounds contained in the skin, especially linalool and 2-phenyl etanol and were impact odorants of Malvasia *aromatica* wine based on odor activity values (OAVs).

**Keywords:** skin-contact, aroma, climate change, white wine, Malvasia *aromatica*

### **1. Introduction**

Skin-contact treatment has been proposed as a technique to try to increase the extraction of varietal aromas from the skins in different white cultivars [1–3]. It is a technique extensively used in the production of young white wines with the aim of improving their intensity and aroma profile by transferring free and glycosidically bound aroma compounds from the grape skins to the must before fermentation begins. The compounds responsible for the varietal aromas of wines depend on grape variety, climate, and soil and will determine the quality and local character of wines. Early winemaking procedures such as skin contact and the amount of pressure applied during pressing together with temperature conditions applied, will affect the extraction of aroma compounds and their precursors into the grape juice and consequently their concentrations in the resulting wine [4–7]. In the course of maceration, the concentration of aromas may increase in the must but there are not always changes at the sensory level in the wines. The varietal characteristics of the wine may be enhanced with the skin contact, however, there is some risk of the

apparition of herbaceous aromas, bitter flavors and excessive color in the musts. For these reasons, the conditions of temperature and contact time between the skins and the juice must be carefully chosen.

The vineyard is a crop with a wide range of adaptation to different environmental and agronomic conditions whose correct development is strongly influenced by the climate. In particular, the suitability of wine-growing areas to reach optimum levels of sugar, pH, color and aromatic components, which are necessary for the production of quality wines, depends on weather conditions throughout the growing period [8, 9]. As a result, climatic fluctuations will make very difficult to produce the same kind of wine in a particular area over seasons. The wines would lose the typicity and distinction of the region being affected the local economy by the decrease of the value of the final product.

The adaptation responses to deal with climate change related effects on winemaking can be implemented at the winery level or at the vineyard level [10]. In oenology, innovations could serve to correct fluctuations in grape quality. Also, can be considered as the first strategy to protect against climate variations related effects by focusing on specific hazards in order to improve the production. These techniques include changes in winemaking practices.

Skin-contact treatment has been proposed as a first measure of adaptation to climate change related effects. This study was focused on variations skin-contact time in order to intensify the aroma potential of winemaking white wines in D.O. "Vinos de Madrid". The purpose of the present paper was to evaluate differences in white musts and wines, which would arise due to different skin-contact time using the same temperature. In particular, the aromatic and sensory characteristics of the wines. To achieve this aim we choose cv. Malvasia *aromatica*, a white grape variety of Italian origin that has been grown in Spain since the 14th century. The main characteristics of this cultivar are: from an aromatic point of view, the presence of terpenes responsible of citrus and floral aromas similar to Muscat varieties [11] and fermentation aroma compounds, mainly fatty acids and their esters, provide it with fruity aromas [3, 12, 13]. On the other hand, physical–chemical characteristics that give rise to musts with high acidity and low pH, which make it a suitable varietal for trying to improve the organoleptic quality of its white wines of D.O. "Vinos de Madrid".

### **2. Material and methods**

#### **2.1 Vintage**

Grapes from *Vitis vinifera* L. cv. Malvasia *aromatica* were hand-collected from an experimental vineyard of the Instituto Madrileño de Investigación y Desarrollo Rural, Agrario y Alimentario (IMIDRA), located in "Finca El Socorro" in D.O. "Vinos de Madrid", Arganda del Rey, Spain (40°8'N, 3°22'W, 715 m altitude). Final harvest time was determined when berries reached 23°Brix and transported to the Experimental Winery from IMIDRA at the "Finca El Encín", in Alcalá de Henares, Spain (40°31'N, 3°17'W, 605 m altitude).

#### **2.2 Skin-contact treatment**

After harvest, grapes were divided into two batches for each assay (1 and 2). One batch was treated in the conventional way (C) without skin-contact and was used as control. In this way grapes were crushed and pressed in a hand-press and 5 g/hl of sulfur dioxide was added. The juice was then settled at 10°C for 12–18 h,

*Influence of Skin-Contact Treatment on Aroma Profile of Malvasia* Aromatica *Wines… DOI: http://dx.doi.org/10.5772/intechopen.99216*

and then racked. The total acidity in the must was corrected with tartaric acid to 6 g/L. The must was racked, dividing the volume equally in three stainless steel tanks. Commercial yeast was added for its fermentation which took place at 16°C and was followed daily by measuring density. The conventional way samples (C) of each assay (1 and 2) were different from each other, they came from different grapes.

For the skin contact treatment, the grapes were destemmed and crushed. The pomace (musts and skin) was mixed 5 g/hl of sulfur dioxide, kept at 10°C for 18 h (A1) and 6 h (A2). At the end were pressed in a hand-press (M18 and M6 assays). The juice was settled, racked and divided as mentioned in the conventional way. The rest of the process was equal to the conventional way.

#### **2.3 Physical-chemical analysis and fermentation kinetics**

Oenological parameters (°Brix, free and total sulfur dioxide, pH, total acidity, volatile acidity, ethanol (% v/v) and residual sugars) were analyzed following OIV official methods [14]. Yeast assimilable nitrogen (YAN) was determined following the Sörensen method.

A daily control of temperature and density was carried out to determine the influence of pre-fermentative skin contact on the kinetics of the fermentations. Fermentation velocity (VF) was measured checking daily the sugar percentage lost during the fermentation. On the other hand, V50 amount of sugar daily transformed by the yeasts when 50% of the sugar content had been used up was also evaluated [15].

#### **2.4 Aromatic analysis of the wines**

Analysis of free aroma compounds was performed by quantification of minor and mayor volatile compounds. Quantification of major volatile compounds was undertaken by GC-FID (Agilent Technologies, Santa Clara, CA, USA) with a DB-Wax column (60 mx 0.32 mm x 0.5 m) from J&W Scientific (Folsom, CA, USA) following the procedures proposed by Ortega [16]. The liquid phase extraction (LPE) of aroma compounds was performed in dichloromethane. The method conditions were: oven temperature 40°C for 5 min, then increased to 3°C/ min up to 200°C, and helium as carrier gas at 2 ml/min. Two mL of aroma extract were injected at 250°C in splitless mode. The total run time was 75 minutes per sample. Analyses were carried out in duplicate.

Minor volatile compounds (terpenoids and C13-norisoprenoids) were determined by HS-SPME/GC–MS following the method proposed by Yuan & Qian [17]. A 50/30 μm DVB/CAR/PDMS fiber (Supelco Inc., Bellefonte, PA) was used for volatile extraction. 20 mL vials were used for chromatography (Agilent Technologies). Two mL of the wine sample were diluted with 8 mL of a citric acid solution (0.5 g/L citric acid, pH 3 saturated with sodium chloride) and 20 μL of 4-octanol (100 μg/L) was used as internal standard were added with a small magnetic stir bar. The vials were capped and equilibrated at 50°C in a thermostatic bath for 10 min. The aromatic compounds were extracted through SPME fiber for 50 min at 50°C with stirring (1000 rpm). The fiber was inserted into the injection port of the GC (230°C) to desorb the compounds. The injection into the chromatograph was manual. An Agilent 6890 gas chromatograph equipped with an Agilent 5973 mass selective detector (Agilent, Santa Clara, CA) was used. Compound separation was achieved with a DB-WAX de J&W Scientific (Folsom, CA, USA) (60 m x 0.32 mm x 0.5 μm film thickness, Phenomenex, Torrance, CA). A constant helium column

flow rate of 1.0 mL/min was used. The chromatographic program was set at 40°C for 3 min, raised to 230°C at 5°C/min for 15 min. Splitless injection mode was used.

### **2.5 Sensory analysis**

Descriptive sensory analyses were performed by a trained panel of 8 people (4 expert tasters and 4 habitual consumers) from the IMIDRA Institute. This panel had been previously trained in the recognition of wine flavor. Sensory descriptive analysis was performed to describe and quantify attributes of the wines based on a scale from 1 (low intensity) to 10 (high intensity). A hedonic classification was also carried out establishing the order of preference of the samples presented. The final score was obtained as the mean of the wine evaluations with their respective standard deviation and interpreted by graphical representation.

### **2.6 Statistical analyses**

The statistical processing of the data was carried out with software SPSS ver. 20.0 (SPSS, Inc., Chicago, USA). Analysis of variance (ANOVA) was applied on oenological parameters, volatile compounds and sensory attributes of the wines. Tukey HSD post-hoc tests were used to establish the significance of differences between means to assess significance (p < 0.05).
